The obtention of vanadium values from vanadium-containing materials is effected in a wide variety of processes. For example, the vanadium-containing material can be subjected to the action of sulfuric acid, sodium oxychloride, hydrochloric acid, nitric acid, etc. In addition, the prior art has also utilized certain ammonium salts such as ammonium chloride, ammonium sulfate, etc., as the precipitating agent whereby insoluble vanadium salts are formed. However, each of the prior art methods possesses certain disadvantages. For example, when utilizing acidic compounds such as hydrochloric acid, nitric acid, sulfuric acid, etc., the problem of clean-up of unwanted chemical compounds necessitates the use of relatively expensive and complicated apparatus in order to avoid the problem of polluting the environment. Furthermore, when utilizing ammonium salts such as ammonium chloride, as exemplified by the method set forth in U.S. Pat. No. 3,320,024 in which ammoniacal ammonium chloride is used to precipitate ammonium metavanadate or ammonium sulfate, etc., the problem of an eventual buildup of chloride or sulfate ions is present. This buildup is unwanted in view of the fact that the mother liquor will, after the caustic leach, eventually contain an amount of salts such as alkali chlorides or alkali sulfates which are of insufficient caustic strength to take the vanadium into solution during the leaching operation.
In contradistinction to this, it has now been discovered that a soluble vanadium value which has been leached with a caustic may be precipitated by utilizing gaseous ammonia in the presence of carbon dioxide which will maintain the pH of the solution in a critical range so that a greater separation of insoluble ammonium vanadates may be obtained than has heretofore been possible.
The invention relates to a process for the recovery of vanadium values from vanadium-containing sources. More specifically, the invention is concerned with an improvement in the process for the recovery of vanadium values whereby greater yields of the desired product may be obtained.
Vanadium values such as vanadium metal or vanadium oxides are useful for many purposes in the chemical industry. For example, vanadium metal may be used as the target material for X-rays, in the manufacture of steel or in the manufacture of vanadium compounds such as catalysts or alloys. Likewise, vanadium oxides such as vanadium pentoxide, are used as the starting material for other vanadium salts, as a catalyst for the oxidation of sulfur dioxide, as a gasoline catalyst, as a catalyst for organic reactions, as a ceramic coloring material, for inhibiting ultraviolet transmission in glass, in black inks, in photographic developers, in dyeing textiles, in medicine, etc.
It is therefore an object of this invention to provide a process for recovering vanadium values from vanadium-containing sources.
A further object of this invention is to provide an improvement in the process for obtaining vanadium values from vanadium-containing sources whereby the process may be effected in a more advantageous economic manner.
In one aspect an embodiment of this invention resides in a process for the recovery of vanadium values from a vanadium bearing source which comprises the steps of: (a) treating a vanadium oxide bearing source with a caustic solution at leaching conditions in a leaching zone, (b) separating the pregnant leach liquor from insoluble tailings, (c) treating said pregnant leach liquor with a soluble ammonium-containing compound and carbon dioxide at precipitation conditions in a precipitation zone, (d) separating the resulting insoluble ammonium vanadates from caustic solution, ammonium compounds and soluble vanadates, (e) stripping said caustic solution to remove ammonia, (f) recycling said stripped caustic solution to said leaching zone, and (g) recovering and treating said solid ammonium vanadates to produce the desired vanadium product.